Early wireless communication was performed in circuit switched (CS) networks, such as Code Division Multiple Access (CDMA) and Global System for Mobile Communications (GSM), with a communication channel dedicated to each call. With the rapid growth of the Internet, technological advances in packet data networks have yielded a packet-based voice communication such as Voice over IP (VoIP). VoIP services are now migrating onto the packet transport networks deployed for the wireless domain such as Wireless Fidelity (WiFi), Worldwide Interoperability for Microwave Access (WiMAX), Wideband Code Division Multiple Access (W-CDMA), High-Speed Downlink Packet Access (HSPDA), and the like.
Internet Protocol based multimedia services are provided over the IMS network and the IMS network includes but is not limited to Wireless Local Area Network (WLAN), CDMA2000, a WiFi and Fixed line. The IMS network supports Voice Over IP (VOIP) service.
A popular advantage of wireless communications is the freedom of mobility. To support mobile communication, the wireless networks perform a function called “handoff.” Handoff, (or handover), is the process by which elements of a mobile network pass a cellular phone conversation or data session from one radio channel in one cell to another radio channel in another cell. It is performed so quickly that callers do not notice. Handoff, unlike roaming, involves moving an active call from one radio to another radio. Roaming involves registering for service/access through different locations on various regional networks, as a mobile station user moves.
In CDMA cellular telecommunication systems, a handoff is usually accomplished via a “soft handoff” between sectors or from one base station to another base station. In a soft handoff between base stations, for example, the mobile station is in communication with more than one base station simultaneously, and thus the mobile station performs a “make before break” transition from one base station to another base station. The soft handoff is possible because in CDMA cellular telecommunication systems, numerous mobile stations communicate with each base station on the same frequency channel, each mobile station having a unique spreading code for distinguishing the information signals broadcast by the numerous mobile stations. Thus, when a mobile station moves from one CDMA cell to another CDMA cell, the same frequency is used in each CDMA cell and the unique spreading code identifies the mobile station to the new base station.
However, when it becomes necessary to handoff between systems, e.g. between systems of different service providers or between systems using different technologies (e.g. between CDMA and AMPS, TDMA or GSM systems), a “hard handoff” occurs. The hard handoff is a “break before make” connection. The hard handoff may be necessary because the available frequency channels or the encoding technologies used in the two adjoining systems differ, and thus when a mobile station moves from one to another, a new frequency channel or coding technique must be implemented.
While handoff of an ongoing call allows a network customer to receive and make calls without interruption during moving, handoff was generally restricted to handoff within the CS network type or within the VoIP network type. From a user's perspective, however, the need to handoff an active call is not limited to handoff between networks of a particular network type.
The deployment of wireless IP network creates a need for a handoff function to handover an active call from one network type to another network type, because it is beneficial to system performance to handoff Access Terminals (ATs) from the CS network to the IP Multimedia Subsystem (IMS) network or from the IMS network to the CS network. For example, the channel conditions associated with one network may be more favorable than the channel conditions associated with the other network due to such factors as fading, adjacent and co-channel interference, and available power at a serving base station (BS). In addition, an operator of both the IMS network and the CS network may desire to move the ATs from one network to the other network for purposes of balancing of system loading or reducing infrastructure costs. Moreover, the AT user wants to handoff his call from the CS network to the IMS network, while roaming or because calling charge in the IMS network is cheaper than in the CS network.
To meet a demand for handoff between heterogeneous networks, Third Generation Partnership Project (3GPP) proposes a standard for handoff of voice call between the CS network and the IMS network in 3GPP TR 23.806. Dual mode ATs which support both the CS network communication and the IMS network communication are introduced as well.
3GPP TR 23.806 requires the dual mode ATs to support voice over both the CS network and the IMS network. To support voice over both networks, the dual mode ATs need to retain handoff configuration information to request a handoff of an ongoing call from the CS network to the IMS network or vice versa. The configuration information includes a Handoff Number (HO Number) which is a public telecommunication number used to handoff an ongoing IP based call from the IMS network to the CS network, and a Handoff Uniform Resource Identifier (HO URI), used to handoff an ongoing call from the CS network to the IMS network.
Several ways to provide HO Number and HO URI to the dual mode ATs have been offered. As one option, the HO Number and HO URI are preconfigured and stored in the dual mode ATs before their distribution to customers. However, the pre-configuration has several shortcomings. When the HO Number or URI for the dual mode ATs change e.g. due to splits of Number Plan Administrators (NPAs), it is necessary to reconfigure HO Numbers and HO URIs programmed the dual mode ATs have to obtain new HO Numbers such reprogramming typically is complex, and it may be difficult to so reconfigure all affected ATs in a timely manner. Moreover, this approach cannot handle regional differences of the HO Numbers and the HO URIs.
Another approach is a configuration of HO Numbers and HO URIs by an adjunct system separate from both CS and IMS network systems. This approach also has a number of drawbacks. First, assignment of the HO Numbers and the HO URIs does not reflect the current load or preferences of VoIP switches serving the dual mode ATs. Second, handoff may be performed based on incorrect HO Numbers and HO URIs which were obtained from the last communication of an AT with the adjunct system, because at the time of a particular call handoff the AT may not yet store correct configuration information depending upon the frequency of communication with the adjunct system. Third, the ATs may be required to support a new protocol to communicate with the adjunct system.
Hence a need exists for a method and a system of providing call handoff configuration information to dual mode ATs, without preconfiguration and/or without need of the adjunct system for assignment of call handoff information.
Another need exists for providing correct call handoff configuration information reflecting any recent change of the information. Still another need exists for providing call handoff configuration information to dual mode ATs using a pre-existing IMS network system, e.g., without the need to deploy an additional adjunct device or the like to update the handoff information.